Crab, slips, and crossed controls

Hey,

Some of you may have heard of Air Canada 143 [http://www.youtube.com/
watch?v=dfJIpA2gv1g] which ran out of fuel in mid air and had to make
an emergency descent at velocities way above the normal limits. The
pilot's makeshift technique was to engage a sideslip to decelerate the
aircraft (which by then had no flaps, and only minimal hydraulics).

Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds. I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.

On Mon, 22 Sep 2008 06:10:03 -0700 (PDT), Amine
wrote:

Hey,

Some of you may have heard of Air Canada 143 [http://www.youtube.com/
watch?v=dfJIpA2gv1g] which ran out of fuel in mid air and had to make
an emergency descent at velocities way above the normal limits. The
pilot's makeshift technique was to engage a sideslip to decelerate the
aircraft (which by then had no flaps, and only minimal hydraulics).

Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds. I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.

all the time to increase the descent angle. not because of bad
piloting mind you.

I was given clearance to land at Parafield once when I came over to
refuel. the clearance was absurd since I was above short base at
1500ft still approaching the circuit but a clearance to land it was
and it was convenient. I side slipped off nearly 1500ft and made it
bang on the numbers. not bang as in splat but 'bang on' as in
precisely at the position (australian idiom)

Sideslips are a very useful tool because they allow you to
substantially increase the drag, which makes you descent like a
plumbers toolbag, but doesnt change the forward speed. so you have no
increased risk of stalling as you wash off the height.

The Gimli glider pilot used the technique for all the right reasons.
Stealth Pilot

On Sep 22, 7:10*am, Amine wrote:
Hey,

Some of you may have heard of Air Canada 143 [http://www.youtube.com/
watch?v=dfJIpA2gv1g] which ran out of fuel in mid air and had to make
an emergency descent at velocities way above the normal limits. The
pilot's makeshift technique was to engage a sideslip to decelerate the
aircraft (which by then had no flaps, and only minimal hydraulics).

Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds. I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.

Slips were in common use for bringing an aircraft down in the days
before flaps, and were taught for that purpose when learned to fly in
the 70's. They work very well. Is that no longer being taught?
--
Gene Seibel
Gene & Sue's Flying Machine - http://pad39a.com/gene/
Because we fly, we envy no one.

Stealth Pilot wrote
Sideslips are a very useful tool because they allow you to
substantially increase the drag, which makes you descent like a
plumbers toolbag, but doesnt change the forward speed. so you have no
increased risk of stalling as you wash off the height.

What you have described is the "forward slip". Although control usage
is the same in both, a "side slip" is used to correct for a crosswind,
and a "forward slip" is used to descend more rapidly on final without
having the airspeed increase. If one is not landing, I suppose that it
would just be a "slip".

Airliners normally do not use either because of the increased discomfort
caused the passengers....both being uncoordinated flight.

Amine wrote:
PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.

AC 143 was constrained by "touchdown speed" runway length. An "emergency
descent" has no such constraint and therefore is able to use the
aircraft's maximum certificated speed for the descent...far in excess of
what would be possible in an approach/landing situation.

In an engine failure situation, keep it as high as possible for as long
as possible to insure that the field can be reached, and then slip as
much as required to lose the excess altitude without gaining airspeed.

Bob Moore
Flight Instructor ASE-IA
ATP B-707 B-727
PanAm (retired)

Robert Moore schrieb:

What you have described is the "forward slip". Although control usage
is the same in both, a "side slip" is used to correct for a crosswind,
and a "forward slip" is used to descend more rapidly

A slip is a slip is a slip.

I always wondered why so many flight instructors celebrate the art of
making simple things seem complicated. I finally came to the conlusion
that it's to look more impressive to the female students.

Stefan wrote
A slip is a slip is a slip.
I always wondered why so many flight instructors celebrate the art of
making simple things seem complicated. I finally came to the conlusion
that it's to look more impressive to the female students.

From The FAA H-8083-3a, Airplane Flying Handbook

INTENTIONAL SLIPS
A slip occurs when the bank angle of an airplane is too
steep for the existing rate of turn. Unintentional slips
are most often the result of uncoordinated
rudder/aileron application. Intentional slips, however,
are used to dissipate altitude without increasing airspeed,
and/or to adjust airplane ground track during a
crosswind. Intentional slips are especially useful in
forced landings, and in situations where obstacles must
be cleared during approaches to confined areas. A slip
can also be used as an emergency means of rapidly
A slip is a combination of forward movement and
sideward (with respect to the longitudinal axis of the
airplane) movement, the lateral axis being inclined
and the sideward movement being toward the low
end of this axis (low wing). An airplane in a slip is in
fact flying sideways. This results in a change in the
direction the relative wind strikes the airplane. Slips
are characterized by a marked increase in drag and
corresponding decrease in airplane climb, cruise, and
glide performance. It is the increase in drag, however,
that makes it possible for an airplane in a slip to
descend rapidly without an increase in airspeed.

A“sideslip” is entered by lowering a wing and applying
just enough opposite rudder to prevent a turn. In a
sideslip, the airplane’s longitudinal axis remains parallel
to the original flightpath, but the airplane no
longer flies straight ahead. Instead the horizontal
component of wing lift forces the airplane also to
move somewhat sideways toward the low wing.
[Figure 8-12] The amount of slip, and therefore the
rate of sideward movement, is determined by the bank
angle. The steeper the bank—the greater the degree of
slip. As bank angle is increased, however, additional
opposite rudder is required to prevent turning.

A “forward slip” is one in which the airplane’s
direction of motion continues the same as before the
slip was begun. Assuming the airplane is originally
in straight flight, the wing on the side toward which
the slip is to be made should be lowered by use of the
ailerons. Simultaneously, the airplane’s nose must be
yawed in the opposite direction by applying opposite
rudder so that the airplane’s longitudinal axis is at an
angle to its original flightpath. [Figure 8-13] The
degree to which the nose is yawed in the opposite
direction from the bank should be such that the
original ground track is maintained. In a forward slip,
the amount of slip, and therefore the sink rate, is
determined by the bank angle. The steeper the bank—
the steeper the descent.

Rgds Bob Moore

Robert Moore schrieb:

A slip is a slip is a slip.

From The FAA H-8083-3a, Airplane Flying Handbook

Ok, so in the USA there exist several different brands of slips.

In the rest of the world however, a slip is a slip is a slip. Which is
how airplanes see it, too, I suppose.

Gene Seibel wrote:
On Sep 22, 7:10?am, Amine wrote:
Hey,

Some of you may have heard of Air Canada 143 [http://www.youtube.com/
watch?v=dfJIpA2gv1g] which ran out of fuel in mid air and had to make
an emergency descent at velocities way above the normal limits. The
pilot's makeshift technique was to engage a sideslip to decelerate the
aircraft (which by then had no flaps, and only minimal hydraulics).

Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds. I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.

Slips were in common use for bringing an aircraft down in the days
before flaps, and were taught for that purpose when learned to fly in
the 70's. They work very well. Is that no longer being taught?

Sure they are still being taught, though the emphasis these days
is in crosswind landings. I think I only did one or two to lose
altitude while a student, the instructors comment being if you
plan properly you seldom need to do this in an airplane with flaps.


--
Jim Pennino

Remove .spam.sux to reply.

wrote:
Gene Seibel wrote:
On Sep 22, 7:10?am, Amine wrote:
Hey,

Some of you may have heard of Air Canada 143 [http://www.youtube.com/
watch?v=dfJIpA2gv1g] which ran out of fuel in mid air and had to make
an emergency descent at velocities way above the normal limits. The
pilot's makeshift technique was to engage a sideslip to decelerate the
aircraft (which by then had no flaps, and only minimal hydraulics).

Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds. I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.
Slips were in common use for bringing an aircraft down in the days
before flaps, and were taught for that purpose when learned to fly in
the 70's. They work very well. Is that no longer being taught?

Sure they are still being taught, though the emphasis these days
is in crosswind landings. I think I only did one or two to lose
altitude while a student, the instructors comment being if you
plan properly you seldom need to do this in an airplane with flaps.



In the mid to late 80's I was doing the first BFR away from my
home-drome and with a CFI I didn't really know and who was younger than
I was (he couldn't have been over 20). I hadn't flown much while at
college and had never landed at the airport where I was getting review.
During my first pattern I was on final and realized I was high and put
the plane into a slip to loose about 100-150'. From the reaction of the
CFI you would have thought I'd just told him his sister was great in
bed. He took over the plane and called a go around. He babbled for a
while about uncoordinated flight and then I realized he had never been
taught to slip for altitude. I told him I'd not ever do it again and we
finished the BFR.

Once we were back on the ground and with his boss close by I left him
reading about them in the FAA Airplane Flying Handbook they had in the
office.

Amine wrote:
Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds. I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

Glider pilots use them on occasion for rapid descent and they are expected
to demonstrate proficiency in them on the practical exam.